Identification and cloning of a mobile transposon from Aspergillus niger var. awamori

Aspergillus niger var. awamori contains multiple copies of a transposable element, Vader. This element was detected as a 437-bp insertion in four independently isolated spontaneous mutants of the niaD (nitrate reductase) gene. The Vader element is present in approximately 15 copies in both A. niger var. awamori and A. niger. A single copy of Vader was detected from only one of the two laboratory strains of A. nidulans which were also examined. Insertion of the Vader element into the niaD gene of A. niger var. awamori caused a 2-bp duplication (TA) of the target sequence. The Vader element is flanked by a 44-bp inverted repeat. The genetic stabilities of the inserted Vader elements at niaD were examined by studying reversion frequencies resulting in colonies able to grow on nitrate as a sole nitrogen source. Mutants niaD392 and niaD436 reverted at a frequency of 9x10(-3) and 4x10(-2), respectively. Two of the mutants, niaD587 and niaD410, reverted at a lower frequency of 6x10(-4).